This is working for me on my iMac (Intel) and v3.1.6 at home and we'll know for sure in Windows at tomorrow's service.
Start HTML: <iframe width="1280" height="720" title="YouTube video player" src="https://www.youtube.com/embed/
End Html: ?rel=0&autoplay=1" frameborder="0" allow="autoplay" allowfullscreen></iframe>
Don't forget to hit the <enter> key when you modify the html; otherwise the changes don't stick.
We've left the controls on, since it doesn't always autostart, the first time you go to the slide. After we start it for testing, it seems to autostart when we go back. We've also left mute alone - see below.
Caution: with v3.1.6, the video also plays, with audio, in the Live panel, so we have to pause it in the live panel. On the plus side, it also plays in the custom stage view we use for someone with limited vision. But the tablet we use for that has to be muted.